Ni/4H-SiC ohmic contact formation using UV nanosecond laser annealing

Abstract Today, global electrification requires new materials for power applications. 4H-SiC dominates the market due to its excellent energy efficiency and wide operating range. This study explores the formation of Ni/4H-SiC backside ohmic contacts using 308 nm nanosecond laser annealing (NLA). After depositing an 80 nm layer of Ni onto 4H-SiC wafers through sputtering, different laser annealing parameters were tested. The energy densities (ED) ranged from 2.4 to 5.4 J/cm², the number of laser pulses applied varied from 1 to 20, and the chuck temperatures from 25 to 400°C. For all series, a common scenario was observed as a function of ED, with initial solid state reactions, then local melting, and finally complete melting and dewetting of the top layer at high ED. An in-depth understanding of the effect of laser conditions on these stages is proposed based on electrical data, Raman spectroscopy, optical microscopy, scanning electron microscopy and transmission electron microscopy cross analysis. Increasing the pulse number and using a heated chuck can substantially lower the energy density (ED) necessary to achieve low-resistance contacts. In addition, trends in sheet resistivity and contact resistivity are related to microstructural evolution during NLA exposure. A contact resistivity of around 5x10-5 Ω.cm² is obtained when the wafer is processed at 25°C. It drops to 10-5 Ω.cm² when processed at 400°C.